In certain applications the need exits to record the rotary motion of revolving parts to establish, for example, the speed, acceleration, delay or direction of rotation and to derive from these data certain control and regulating functions. Devices of this kind are used in particular in so-called antilocking systems in motor vehicles for the optimum regulating of the braking power. However, they are also used in positioning devices where a driven part must be placed precisely in a target position. Generally, this involves a step counter which turns with the rotating part and is equipped with an angle code which is scanned by a sensor and emits a signal per angle unit which is sent to a connected electrical circuit for interpretation.
A similar device for recording revolutions is known from, e.g., GB-PS 16 04 862. In that instance, a metal race--whose circumference is equipped with gear teeth--is placed on the inner race of a ball bearing. A sensor is held by an annular element attached to the outer race of the bearing in such manner that the sensor head is immediately adjacent to the teeth. The annular element which supports the sensor head is rigid and forms a labyrinth seal together with the metal annular gear, or it consists of a flexible sealing ring which has a sealing lip which slides against a smooth face of the metal annular gear. The teeth passing before the scanning head of the sensor trigger a pulse train whose frequency is a measure of the immediate angular velocity.
Although this known device combines in a single component the necessary mechanism for determining the rotary motion and a sealed bearing, it requires an additional element in the form of an annular gear, and the annular element which assumes the sealing function is a complicated--and thus expensive--component. In addition, the conditions resulting from the special design make it impossible to use commercially available and tested standard sealing rings in the bearing.